Panel air filters having a multiple V-pleat configuration are commercially available from various sources such as Donaldson Company, Inc., Pall Corp., TriDim Filter Corp., and Koch Filter Corp. A partial section of a multiple V-pleat panel, having a constant pleat height, is shown in FIG. 1. Multiple V-pleat panel configurations are known to greatly improve performance in a panel filter having an axial flow configuration.
It is well established in the filter industry that by decreasing pleat height and increasing pleat density, additional media surface area can be packaged into a given volume, thereby lowering face velocity, which is a function of media surface area. Such is the basis for multiple V-pleat panel filters. However, in some applications, a panel filter is not desirable. For example, when air is drawn from a large plenum into an outlet duct, a cylindrical, radial flow filter is the preferred configuration, in order to increase filter media surface area.
Previously, there have been no known attempts to use a constant pleat height multiple—V-pleat configuration in a cylindrical arrangement. The disadvantages associated with such a design would prevent those skilled in the art of filters from attempting such a design. The disadvantages include a decrease in the amount of media that can be packaged within a given volume, and an increase in pressure loss that results from both the higher flow velocities across the media face and the additional inlet and outlet losses at the “V's”.
A commercially available oil filter, produced for Toyota by Nippondenso, incorporates variable pleat height with multiple V-pleats in a cylindrical configuration. This design is also shown in FIG. 17 of U.S. Pat. No. 4,746,432, assigned to Nippondenso. The general filter media configuration of FIG. 17 of the '432 patent is reproduced as FIG. 2 of this application.
Another variable pleat height construction has pleats that have one common edge along a line that is perpendicular to the pleats. An example of this has been found on an Internet web site, and is typical of a panel filter element that can be produced on a programmable pleater, such as available from Rabofsky Company. An example of this can be found at “http://www.alps-filter.co.jp/alps-e/preets.htm” and is shown in FIG. 3.
As mentioned above, there have been no known attempts to use a constant pleat height multiple V-pleat configuration in a cylindrical arrangement. A schematic diagram of a cylindrical arrangement of a constant pleat height multiple V-pleat filter is shown in FIG. 4, with the individual pleats omitted. Because the outer circumference of the filter is greater than the inner circumference, the outer “V” angle is much greater than the inner “V” angle when a constant pleat height is used. This results in a large space penalty for this configuration.
A better cylindrical filter design is needed.